A plane formed by two perpendicular number lines is called a Cartesian plane. The number lines are called axes. The horizontal axis is called the x-axis and the vertical axis is called the y-axis. The point of their intersection is called the origin and the four planes formed are called quadrants. The axes can be used to describe any point in the plane using an ordered pair of numbers called coordinates. The coordinates is represented by (x,y). The first number, x, gives the point's horizontal position and the second number, y, gives its vertical position. All positions are measured relative to a "central" point called the origin, whose coordinates are (0,0). NOTE: Other names for Cartesian plane is X-Y plane, Cartesian Coordinate Plane, Two-dimensional Coordinate System or simply Coordinate plane.